The term "cluster tool" generally refers to a modular, multichamber, integrated processing system having a central wafer handling module and a number of peripheral process chambers. Cluster tools have become generally accepted as effective and efficient equipment for manufacturing advanced microelectronic devices. Wafers are introduced into a cluster tool where they undergo a series of process steps sequentially in various process chambers to form integrated circuits. The transfer of the wafers between the process chambers is typically managed by a wafer handling module located in a central transfer region. Typically, cluster tools are of two different types: single wafer processing or batch wafer processing. Single wafer processing generally refers to a chamber configuration in which a single wafer is located for processing. Batch wafer processing generally refers to a chamber configuration in which multiple wafers are positioned on a turntable and are processed at various positions within the chamber as the turntable rotates through 360.degree.. A cluster tool configured for batch processing allows multiple wafers, typically from four (4) to seven (7) wafers, to be simultaneously processed in a single chamber.
FIGS. 1, 2A, and 2B show examples of commercially available batch processing systems 10. FIG. 1 is a top schematic view of a radial cluster tool for batch processing that is available from Novellus Corporation. This cluster tool includes two batch processing chambers 12, 13 that each hold six wafers for processing. A single wafer handling robot 16 located in a transfer chamber 18 is used to transfer wafers from a loadlock chamber 20 to a first batch processing chamber 12 one by one, where the wafers are sequentially received on a turntable 22 before receiving the same processing steps. The wafers may then be transferred, one by one, to a second batch processing chamber 13, where the wafers undergo additional processing steps. Typically, wafers are loaded into the system one at a time and moved into a chamber where they receive partial processing at various positions as the wafers are rotated 360.degree. on the turntable.
FIGS. 2A and 2B are top and side schematic views of a cluster tool 10 for batch processing that is available from Mattson Technology. The loadlock chamber 20 and transfer chamber 18 have a common wafer elevator 19 that allow the wafers to be staged within the transfer chamber. A transfer robot 16 transports wafers to the processing chamber, such as a chemical vapor deposition (CVD) chamber, which holds up to four wafers. The wafers are then returned to the wafer elevator and eventually withdrawn from the tool.
One disadvantage of batch processing, including the processing performed in the cluster tools described above, is that batch processing frequently provides poor deposition uniformity from the center of the wafer to the edge of the wafer. Process uniformity is important in order to obtain uniformity of deposition on the wafer. The poor uniformity of batch processing systems is a direct result of having multiple wafers being partially processed at multiple stations within a single chamber.
An alternative approach to improve process uniformity is the use of single wafer processing chambers. Single wafer processing is generally considered to provide a higher degree of control over process uniformity, because a single wafer is positioned in a process chamber where it undergoes a complete process step, such as a deposition step or an etch step, without having to be moved to a different position. Furthermore, the components of a single wafer processing chamber can be positioned concentrically or otherwise relative to the single wafer.
FIG. 3 shows a top schematic view of a cluster tool 10 having multiple single wafer processing chambers 12 mounted thereon. A cluster tool similar to that shown in FIG. 3 is available from Applied Materials, Inc. of Santa Clara, Calif. The tool includes a loadlock chamber 20 and a transfer chamber 18 having a wafer handling module 16 for moving the wafers from location to location within the system, in particular, between the multiple single wafer processing chambers 12. This particular tool is shown to accommodate up to four (4) single wafer processing chambers 12 positioned radially about the transfer chamber.
There is a need for a vacuum processing system that provides both uniform wafer processing and high throughput. More particularly, there is a need for an integrated system and process chambers that work in cooperation to incorporate single wafer architecture with batch wafer handling techniques. It would be desirable to have a system with a small footprint/faceprint and which requires lower capital investments and operating costs than typical cluster tools.